Field of the Invention
The present invention relates to a lustrous coating material composition, and also to a lustrous resin film and a multilayer coating film obtained by using the lustrous coating material composition.
Related Background Art
Conventionally, effect pigments in which a titanium oxide layer is provided on a surface of a flaky material such as natural mica, synthetic mica, or flaky alumina have been used in many fields. These effect pigments have strong luster and a grainy texture (glittering luster), and are used as pigments for providing a pearl-like luster. To obtain an effect pigment which has a grainy texture-free silk-like luster, so called a silky texture, and which can provide a high quality design in contrast to the above-described effect pigments, the improvement of a flaky titanic acid (titania nanosheets) and/or a resin used has been attempted.
As an effect pigment capable of providing such a silky texture, Japanese Unexamined Patent Application Publication No. 2006-257179 (Patent Document 1) discloses an aqueous effect pigment dispersion containing a flaky titanic acid (titania nanosheets) in which interlayer swelling or delamination is caused by treating a layered titanic acid compound with an acid and then with an organic basic compound. In addition, Japanese Unexamined Patent Application Publication No. 2000-344520 (Patent Document 2) describes a flaky titanic acid useful as an additive for a coating material or the like and a method for producing the flaky titanic acid. Further, Japanese Unexamined Patent Application Publication No. 2006-305515 (Patent Document 3) discloses a multilayer coating film having a base layer containing a flaky titanic acid (flaky titanic acid pigment) and being excellent in anti-chipping property. Conventional resin films containing the flaky titanic acids as described in Patent Documents 1 to 3 have a good silky texture with a high luster, but do not necessarily have sufficient adhesion.
Meanwhile, such an effect pigment containing a flaky titanic acid has a problem in that when a coating film, especially, a multilayer coating film, is formed for a vehicle exterior by using the effect pigment, the coating film tends to easily undergo local peeling. Because of the high hydrophilicity, the flaky titanic acid interacts weakly with resins, which are generally hydrophobic. For this reason, the adhesion of the flaky titanic acid to a resin is weak, and adhesion sufficient for a coating film cannot be obtained. Actually, it has been known that the delamination occurs at titania interlayers where no resin layers are present.
As coating material compositions capable of improving the adhesion, Japanese Unexamined Patent Application Publication No. 2012-241072 (Patent Document 4) discloses a lustrous coating material composition containing a flaky titanic acid and an amino group-containing acrylic resin having an amine value of 0.05 to 0.3 mmol/g-solid, and Japanese Unexamined Patent Application Publication No. 2015-7173 (Patent Document 5) discloses a lustrous coating material composition containing an acrylic resin and a flaky titanic acid to which a urethane resin is bound.
However, recently, such a lustrous coating material composition has been required to have increasingly higher levels of properties, and there has been a demand for a lustrous coating material composition capable of forming a lustrous resin film which has a good silky texture with a high luster and which has not only an initial adhesion but also a better water-resistant adhesion with the occurrence of peeling being sufficiently suppressed.